Various wireless communications networks offer features or specifications aimed at the efficient delivery of multimedia or other data formats on a multicast or broadcast basis. These networks include Universal Mobile Telecommunications System (UMTS) wideband Code Division Multiple Access (WCDMA) networks, which may be specified by 3GPP (3rd Generation Partnership Project), 3GPP2, ETSI (European Telecommunications Standards Institute), and/or the Institute of Electrical and Electronics Engineers (IEEE).
For example, an IEEE 802.16e specification defines a Multicast Broadcast Service (MBS), which exploits “single frequency networking” (SFN) principles to deliver service (e.g., mobile television) on an efficient, wide area basis. In an SFN network, multiple transmitters simultaneously send the same signal over the same frequency channel. High levels of spectral efficiency may be achieved for a broadcast or multicast service by simulcasting, on a fully time-synchronous and frequency-synchronous basis, shared Medium Access Control (MAC) layer Protocol Data Units (PDUs) using a common or identical set of radio resources in each cell. This may provide high orders of downlink macro-diversity (e.g., where multiple base stations transmit the same signals), which when combined with a lack of in-band interference, may lead to elevated receiver Signal-to-Noise Ratios (SNRs). These techniques may be capable of supporting relatively high modulation orders and forward error correction encoding rates.
In some systems, SFN techniques are associated with Orthogonal Frequency Division Multiplexing (OFDM) methods of wireless network multiple access. Other air interface specifications, such as the 3GPP2 Broadcast and Multicast Services (BCMCS) feature, seek to hybridize OFDM and CDMA approaches to air interface design by multiplexing components of a legacy CDMA air interface and an OFDM-based broadcast network on a Time Division Multiplexing (TDM) basis. For example, SFN methods may be applied to direct sequence CDMA networks, as exemplified by a 3GPP specification entitled “A Backward Compatible CDMA-Based Enhanced Broadcast Multicast (EBM) System for HRPD,” 3GPP2 Technical Specification Group C, October 2004, C30-20041019-011.
Techniques for broadcast and multicast service delivery are also defined for networks based solely on CDMA principles in the absence of SFN methods. For example, the Multimedia Broadcast Multicast Service (MBMS), as part of the 3GPP Release-6 specifications, uses diversity techniques, such as soft symbol combining or selection combining for efficient transfer of data (e.g., multimedia content) to multiple user equipments (UEs) in a point-to-multipoint fashion. Methods of downlink macro-diversity that are based on soft combining or selection combining techniques generally may not be able to approach the receiver SNR's achievable using SFN methods.
Another proposal entitled “Dedicated MBMS Carrier Using Common Transmitted Waveforms,” 3GPP TSG-RAN WG1 Meeting #46, August 2006, R1-062268 (herein “R1-062268”), applies an SFN approach to the 3GPP MBMS service. Specifically, R1-062268 proposes that only an orthogonal primary common control physical channel (P-CPICH) and one or more secondary common control physical channel (S-CCPCH) be transmitted by each participating base station (BS), in a time-synchronous and frequency-synchronous fashion, in a downlink spectrum cleared of interfering unicast transmitters or other radiators (e.g., the downlink spectrum is dedicated to MBMS). R1-062268 also proposes that each BS scramble its transmission using a common scrambling code. This approach may permit higher receiver SNRs to be achieved, and generally may improve wide-area broadcast channel spectrum efficiency However, this approach suffers from at least three major drawbacks.
First, according to R1-062268, primary synchronization channel (P-SCH) and secondary synchronization channel (S-SCH) symbols are not transmitted on the dedicated MBMS carrier frequency. Due to the lack of a synchronization channel on the dedicated MBMS carrier, UEs are forced to camp on, and extract synchronization information from, a companion unicast network. This may be inefficient and time-consuming, and may render redundant significant components of established and high performance UE P-SCH and S-SCH acquisition hardware.
A second drawback pertains to an argument, in R1-062268, that current wireless CDMA (or WCDMA) receiver architectures can deal with the increased channel time dispersion resulting from SFN operation without a major re-working of the receiver design. However, the increase in delay spread in networks with contemporary cell radii does not support this argument. Third, channel estimation using a code-division multiplexed pilot signal (e.g., a pilot signal based in the P-CPICH symbol) is susceptible to significant intra-cell interference in multi-path channels. This may be more pronounced in the case of an SFN channel with its increased median root mean square (RMS) delay spread, and may warrant further modification or enhancements of the current 3GPP Common Pilot Channel (CPICH) structure.
It is desirable to provide a solution that enhances the achievable receiver SNR of current wireless multicast and/or broadcast air interface designs (e.g., the 3GPP WCDMA Release-6 MBMS). In addition, it is desirable to provide a solution that does not warrant the deployment of additional synchronization equipment in BSs, and that permits UEs to access a dedicated enhanced MBMS carrier without having to access a companion unicast network. Additionally, it is desirable to provide a solution that enables sufficient channel estimation SNR to sustain higher spectrum efficiency in the broadcast service. In addition, it is desirable that a 3GPP MBMS specification evolution permit substantial re-use of existing terminal designs.
Other desirable features and characteristics of the present inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background.